Original contribution
Ultrasonic quantitation of superficial degradation of articular cartilage

https://doi.org/10.1016/j.ultrasmedbio.2004.03.005Get rights and content

Abstract

Ultrasound (US) has been suggested as a means for the quantitative detection of early osteoarthrotic changes in articular cartilage. In this study, the ability of quantitative US 2-D imaging (20 MHz) to reveal superficial changes in bovine articular cartilage after mechanical or enzymatic degradation was investigated in vitro. Mechanical degradation was induced by grinding samples against an emery paper with the grain size of 250 μm, 106 μm, 45 μm or 23 μm. For enzymatic degradation, samples were digested with collagenase, trypsin or chondroitinase ABC. Variations of the US reflection coefficient induced by the degradation were investigated. Furthermore, two novel parameters, the US roughness index (URI) and the spatial variation of the US reflection coefficient (SVR), were established to quantitate the integrity of the cartilage surface. Statistically significant decreases (p < 0.05) in US reflection coefficient were observed after mechanical degradations or enzymatic digestion with collagenase. Increases (p < 0.05) in URI were also revealed after these treatments. We conclude that quantitative US imaging may be used to detect collagen disruption and increased roughness in the articular surface. These structural damages are typical of early osteoarthrosis. (E-mail: [email protected])

Section snippets

Introduction and literature

Osteoarthrosis (OA) is one of the most challenging joint diseases that threaten the human locomotor system (Buckwalter and Mankin, 1997, Elders, 2000). In OA, the articular surface degenerates, probably through the disruption of the superficial collagen network (Buckwalter and Mankin 1997). Earlier studies have demonstrated that the superficial tissue layer contributes significantly to mechanical behaviour of cartilage (Guilak et al., 1994, Korhonen et al., 2002) and is, therefore, important

Sample processing

Bovine knee joints (n = 44) were obtained from the local slaughterhouse (Atria Oyj, Kuopio, Finland). Knee joints were opened and two different groups (Fig. 1) of osteochondral samples were prepared from the patellae within 5 h post mortem: the samples in group 1 (n = 26, diameter = 6 mm) were subjected to mechanical degradation and the samples in group 2 (n = 18, diameter = 16 mm) to enzymatic degradation. For both groups, US images of each sample were obtained before and after degradation.

Results

Mean values (± SD) of all the US parameters are presented in Table 1. After mechanical grinding, US reflection coefficients R and IRC decreased (p < 0.05) with all four emery paper grades. Furthermore, the URI increased (p < 0.05) after mechanical grinding with all emery papers (Fig. 4). The spatial variation of the US reflection coefficicent (SVR) increased (p < 0.05) only with paper-60. A moderate linear correlation was found between URI and IRC in samples before and after mechanical

Discussion

In the present study, we investigated the ability of high-frequency ultrasonic 2-D imaging to detect the superficial changes after mechanical or enzymatic degradation of bovine articular cartilage in vitro. Reflection at the cartilage surface was quantified, and the changes induced by degradation were evaluated. Furthermore, novel parameters for estimation of cartilage surface roughness (URI) and spatial variation of US reflection (SVR) were introduced. Measurements of the US reflection

Acknowledgements

Financial support from the National Technology Agency (TEKES, project 40714/01), Finland; Kuopio University Hospital (EVO, project 5173), Kuopio, Finland; the Finnish Cultural Foundation of Northern Savo, Finland and the Finnish Graduate School in Skeletal Diseases is acknowledged. The authors thank Heikki Nieminen, University of Kuopio, for technical assistance and Professor Heikki Helminen, Department of Anatomy, University of Kuopio, for his constructive criticism.

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